Audio cardioscope



1966 M. E. CROSLIN 3,233,041

AUDIO CARDIOSCOPE Filed July 25, 1962 2 Sheets-Sheet 1 FIG] INVENTOR.

Michael E. Croslin ATTORNEY MICRO- PHONE Feb. 1, 1966 E. CROSLIN3,233,041

AUDIO CARDIOSCOPE Filed July 25, 1962 F|G.6 FIG. 7

2 Sheets-Sheet 2 INVENTOR.

60 Michael E. Croslin ATTORNEY United States Patent 3,233,041 AUDIOCARDIOSCOPE Michael E. Croslin, Forest Hills, N.Y., assiguor to Cros-Dorf Associates Ltd., Hempstead, N.Y., a corporation Filed July 25,1962, Ser. No. 212,334 6 Claims. (Cl. 1791) This invention relates tostethoscopes and particularly to electronic stethoscopes, oraudio-cardioscopes, which utilize a microphone or sound-sensitivetransducer for performing the auscultation or examination of the chestand back for internal sounds that characterize and record the conditionof internal organs. By the use of such a sound-responsive transducer, asignal may be derived which may then be amplified for better hearing.

The primary object of the invention is to provide a stethoscope whichwill convert the internal body sounds into an electrical signal whichmay then be utilized to 0p erate a suitable receiver to reproduce asound corresponding substantially to the original sound as detected.

To be suitable for use in a stethoscope, the sound-responsivetransducer, or microphone, should be substantially linear in itsresponse to vibrations from a range of practically zero to an upperlimit of about 800 cycles per second. The transducer should actually beable to detect frequencies as low as two cycles per second.

The transducer must be relatively light in weight since it must behandled and manipulated for positioning at different parts of the bodywith relative ease. The transducer and its housing must therefore berelatively light in weight. The transducer must therefore be relativelysmall, and one of the characteristics of the smaller transducer is thatits range of operation tends to be in a higher frequency range. That isone of the problems that must therefore be overcome in utilizing andapplying a microphone as an acousto-magnetic transducer in astethoscope. Another problem that is encountered in small microphonesutilizing the fixed core magnet and a voice coil with a sound-responsivevibratable armature that varies the reluctance of an air gap between thecore and the armature, is that the armature which must be of relativelythin magnetic material will have a resonance characteristic that willpeak somewhere within the operating range desired for the device in astethoscope.

Another object of the invention and one of the important featuresthereof, is the provision of a modified transducer, in which thearmature as the sound-responsive element, is appropriately mass-loadedso the resonance characteristic of such mass-loaded armature will beshifted to the region below two cycles per second, so that the responsecharacteristic of the transducer will not be distorted by the resonancecharacteristic of the vibratable armature.

Another object of the invention is to provide a stethoscope with atransducer and related amplifier, which will be automatically placed inoperating condition when the transducer is placed against a selectedarea of a human body being examined, and which will automaticallydisconnect and tie-energize the circuitry of the transducer and theamplifier when the transducer is removed from the contact area of thehuman body, thereby preventing a needless drain on the battery supplyutilized with the stethoscope of the present invention.

Another object of the invention is to provide a transducer in which thevibratable armature of the transducer is directly physically coupled tothe human body under examination, so that sound vibrations from thehuman body are transmitted directly and physically to the vibratablearmature, without any intervening air columns as is found in the presentconventional air-type stethoscope.

A feature of the invention is the disposition of the auxiliary massloading on the vibratable armature in position where it may also beutilized as the coupling means for physically and sonically coupling thevibratable armature of the transducer to a small area of the human bodyadjacent the region of the body under examination.

A further object of the invention, and an important feature thereof, isthe utilization of the auxiliary mass both as a coupling and as apositioning element for the vibratable armature, to place the vibratablearmature in a more efiicient operating position adjacent the polarelements of the core, in order to reduce the air gap between the coreand the armature to a minimum dimension, thereby increasing thesensitivity and efficiency of the transducer.

A further feature of the invention is the disposition of the auxiliarymass on the vibratable armature in the form of a co-axial projectionfrom the armature, formed symmetrically around the axis and shaped withits front end of relatively small area, either as a point or as a curvedsurface, to establish a minimum area of contact on the skin of the humanbody to which the transducer may be applied during examination.

Another object of the invention is to provide in the amplifying systemfor the transducer, means for varying the frequency response of theamplifier, in order to accentuate a certain range of frequencies, as atone control device, and also to provide a simple means whereby theexamining physician may also selectively vary the amplification of theamplifying system by a simple operation of a dial by his thumb on asimple rotary control knob available at the rear surface of thetransducer housing alongside the handle.

As another feature of the invention, it has been found that the use ofaluminum for the auxiliary mass and coupling element between thevibratable armature and the human body being examined has provided bestresults.

The general arrangement of the elements of the stethoscope, and thefeatures of construction of the microphone and of the housing forsupporting and manipulating the microphone transducer to position thetransducer at any selected part of a human body are described in thefollowing specification and shown in the accompanying drawings, in whichFIGURE 1 is a perspective view showing the various elements of thestethoscope in accordance with the present invention;

FIGURE 2 is a schematic sectional view of the microphone transducer,unmodified;

FIGURE 3 is a schematic view of the microphone of FIGURE 2 as modifiedin accordance with the principles of this invention to add an auxiliarymass to the vibrating armature or membrane of the microphone, showingthe relative positions of the elements before the microphone is pressedagainst a human body;

FIGURE 3A is a view similar to FIGURE 3 showing how the skin of thehuman body engages the front end point of the auxiliary mass to pressthat auxiliary mass and the armature diaphragm or membrane towards thecore to the limited extent permitted by a stop element;

FIGURE 4 is a side elevational view of one form of auxiliary mass shownin its co-axial application to the vibratable armature of themicrophone;

FIGURE 5 is a modified form of the auxiliary mass shown in itsapplication to the armature which may be in the form of a disc for themicrophone;

FIGURE 6 is a side elevational view of the housing for the transducerand the amplifier components, with the side wall of the housing brokenaway to expose and show the various components within the housing;

FIGURE 7 is a rear elevational view of the housing I a unit of FIGURE 6with the rear wall broken away to expose the components supported withinsaid housing;

FIGURE 8 is a circuit diagram of the system.

As shown in FIGURE 1, a stethoscope 20, constructed in accordance withthe principles of this invention, is shown as comprising a manuallyoperable handle housing containing a microphone for placement against ahuman body to be examined, and containing further the components of anamplifier system including batteries for andplifying an electricalsignal generated at the microphone by sounds emanating from the humanbody. A cable of conductors carries the amplified signal from thecomponents within the housing 25 to the ear pieces shown as tworeceivers 32 and 35 supported on a suitable bail 36 to support the tworeceivers 32 and 34 in appropriate positions for insertion in theexamining physicians ears.

The housing 25 is provided with an opening 35 adjacent its front upperend directly behind which is supported the microphone transducer bymeans of which the sounds Within a human body are heard and caused togenerate a signal voltage in a suitable voice coil for subsequentamplification and reconversion into sound signals at the two ear piecereceivers 32 and 34. The lower end of the housing 25 is formed inappropriate shape and dimensions to serve as a handle for manipulatingthe housing 25 to press the upper end 35 to any portion of the humanbody at which the auscultation or listening operation is to beperformed.

In FIGURE 2 is shown schematically the general basic construction of amicrophone of the type utilized, designated at 40, and shown comprisinga circular magnetic core 42, an armature 44, which for the presentpurposes consists of a circular diaphragm or disc, with a voice coil 46disposed in the annular well 48 between the core center post 42A and theconcentric annular ring portion 42B. The terminals of the voice coil 46are represented at the terminal posts 47. The core 42 is supported andenclosed in a concentric housing 50 of non-magnetizable metal such asbrass, to avoid any magnetic interference with the operation of thepermanent magnet core 428 and the magnetizable disc 44. The brasshousing 50 is provided with a suitable shoulder or ledge 52 to supportthe rim of the diaphragm disc or armature 44. The armature disc 44 ispreferably relatively free at its outer circular edge and is heldagainst displacement or falling out of its seat by a simple washer 54 ofany suitable material that may be snapped into position in the groove 55in the side wall 56 adjacent the ledge of the brass housing 54 of themicrophone.

As was previously mentioned, the dimensions of the microphone should berelatively small, in order to present a minimum of weight together withall of the other components in the housing handle which must bemanipulated by the physician with relative freedom.

For example in the microphone utilized in the present invention, theoverall dimensions of the assembly as shown in FIG. 2, are 0.775 inchdiameter of the housing bracket 50 and 0.240 inch depth of the housing50.

In FIGURE 3 is shown schematically, the elements entering into themodified microphone 60 constructed in accordance with the principles ofthe present invention. In addition to the elements shown in the basicmicrophone assembly in FIGURE 2, the modified microphone 60 of FIGURE 3includes additionally an auxiliary mass 65 secured to the diaphragm 44in a position where the mass projects co-axially from the center of thedisc 44, in the manner shown. A positioning and pressure plate 70 isshown supported on the brass housing 50. For simplicity, the pressureplate '70 is shown resting on an outer ledge 72 concentric around themain axis 75 of the transducer 60.

The pressure plate 70 is provided with an opening 76 symmetrical aboutthe axis 75. The co-axial dimension of the auxiliary mass 65 is such asto bring the front end point 65A of the mass into the opening 76 to aplane at iwhich the point A will be engaged and pressed backward by thesurface 78 of the skin of the human body 80 against which the frontpressure plate of the microphone is pressed during the auscultationexamination.

In the normal position of the diaphragm 454 of the microphone 60, themass 65 is in raised or forward position, at which time the air gap 42Cbetween the armature diaphragm disc 44 and the center core pole 42A ismaximum. Under such free condition, the mass 65 in its forward positionis also forwardly spaced from a limit stop element 84 which limits thebackward movement of the mass 65 when pressed against the skin of thebody 30, so the air gap 42C may be reduced to a minimum while assuringthe existence of an air gap at 42C between the armature 44 and the polarelement 42A. The limit stop 84 is shown for simplicity as mounted on thepressure plate '70, but may be equally well mounted on the top surfaceof the brass housing 50 as a support.

When the microphone of FIGURE 3 is pressed against the body duringexamination, the surface of the skin at 7 8 will project into theopening 76 of the pressure plate 70 a small distance, as indicated inFIGURE 3A, sufiiciently to accomplish the inward movement of the mass 65to engage the limit stop 84 and to press the diaphragm 44 to closerspacing to the polar element 42A.

By way of example, when the diaphragm 44 is thus pressed to the pole 42Afor operating condition, the air gap spacing between the diaphragm andthe pole 42A is of the order of 0.002 to 0.005 inch. The limit stop 84represents schematically one way of assuring such air gap spacing. Otherprocedures may be resorted to for assuring such air gap spacing, such ascopper plating the end face of the polar element 42A so the center ofthe armature 44 may actually by physically placed against the polarelement 42A and separated therefrom by the nonmagnetic layer of copperor the like.

FIGURE 4 shows a side elevation of the auxiliary mass element 65co-axially secured to and mounted on the armature diaphragm or disc 44so the auxiliary mass 65 is essentially an integral part of thediaphragm. The dimension of the auxiliary mass 65 may be realized fromthe fact that the top button 65A is 0.700 inch in diameter and the base65B is 0.280 inch in diameter.

In FIGURE 5 is shown another form of mass which has been successfullyemployed in the modified microphone of this invention. This secondmodification 85 of the mass element as shown in FIG. 5 has a totalheight of 0.250 inch, the same as the mass 65 in FIG. 4, and the base853 is also of the same diameter as the base 658, namely 0.280 inch. Thetip 35A has a diameter of 0.120 inch, with the curvature at the frontend on a radius of 0.060 inch. While the two auxiliary mass buttons 65and 85 may be formed of any suitable sound-conducting material that willconvey the sound waves from the human body being examined to thevibratable armature disc 44, the use of aluminum alloy 2024-T4 in thedimensions specified have provided excellent results. A second aluminumalloy 5052 H-34 has also exhibited excellent characteristics inconnection with the magnetic diaphragm 44.

In each case the auxiliary mass 65 or 85 of FIG. 4 or FIG. 5 has serveda double purpose. First the auxiliary mass has increased the effectivemass of the assembly of the vibratable disc and the auxiliary massbutton sufficiently to shift the resonance characteristic of theassembly of the vibratable disc and the auxiliary mass to a relativelylow frequency value beyond the lower limit of the desired range ofoperation for the desired detection and observation of the sounds withinthe human body.

For example, in a micro-phone unit as shown in FIG. 2, with thedimensions previously specified the range of effective operation wasbetween 30 cycles at the lower end of the range and 3,000 cycles at theupper end of the range. A resonance peak occurred at about 500 cyclesper second, which was practically at the mid-point of the desired rangeof operation for an auscultation examination.

However, with the application of the auxiliary mass button 65 as shownin FIG. 3, the resonance region was actually shifted to a point below 2cycles per second, thereby rendering the operation of the microphonewhen modified as in FIG. 3, substantially linear over the range desiredfor complete auscultation examination.

FIGURE 6 shows an internal side view of the microphone housing 25 whichhas an upper cavity 100 and a lower cavity 102. The upper cavity 100 isprovided with an outwardly inclined front wall 104 which blends into thebottom front wall 106 and two side walls 107 and 108 to define a hollowtapered boss 110 inclined at an obtuse angle to define and locate afront supporting flange 112 upon which the microphone transducer 60 maybe suitably coaxially supported to enable the lower handle portion ofthe housing 25 to be easily manipulated to press the microphone assembly60 against a human body while leaving the fingers of the hand free tomove the housing unit and the microphone without frictionally engagingthe body by the fingers of the hand.

The front flange 112 defines an opening 114 for supporting a rubber cup116 that is cylindrical in shape and serves to support the microphoneassembly in slightly projected position to permit the auxiliary massbutton of the microphone to be engaged by the skin in the area of thehuman body against which the pressure plate 70 is pressed.

The cup 116 referred to as a rubber cup may be made of any othersuitable material, such as, for example, Teflon, or vinyl plastics,which may be molded or shaped to provide a suitable support for themicrophone with a characteristic that will be appropriate to damp anyvibrations that might arise in or be transmitted through the housing 25.

The rubber cup 116 for supporting the transducer assembly 60 is shown asconsisting of an external cylinder 116A and an internal re-entrantcylinder 116B terminating in a front ring portion 116C of reduceddiameter for tightly gripping the side wall of the front pressure plate70 of the microphone assembly 60. The outer cylinder of the transducercup 116 terminates in a front seating flange 116D an a ring wedge 116Ewhich cooperates with the flange 116D to grip the flange 112 whichcircles and defines the opening 114 through which the microphoneassembly 60 projects for engagement with a body to be examined.

A bracket 120 is secured and anchored to two bosses 122A and 1223secured to or integrally formed on the inside of the housing 25. Thebracket 120 carries the microphone assembly 60 and a single-polesingle-throw switch 125 co-axially disposed behind the microphoneassembly 60, so the slight pressure employed to press the transducerfront pressure plate against a human body will be sufficient to operatethe switch 125. That switch may be of any conventional type that may beoperated by a short axial movement of an operating pin, with appropriateleverage arm to multiply the short movement of the complete microphoneassembly in its supporting rubber cup 116.

As previously indicated in the description of FIG- URE 3, a suitablestop element is provided for the auxiliary mass button 85 shown in thisFIGURE 6, and further pressure movement of the entire microphoneassembly 60 within its supporting cup then provides the additionalmovement necessary to operate the switch 125.

The backward movement of the transducer assembly 60 to operate theswitch 125 is also limited by a suitable stop pin so that the frontpressure plate 70 will remain suitably engaged with the area of the bodybeing examined without moving backwards sutficiently to enable the frontsurface of the flange 116 to engage the surface of the body.

The stop pin for limiting the backward movement of the microphoneassembly 60 is shown by an auxiliary bracket 127 pivotally mounted onthe main bracket for the entire microphone and switch assembly. Theauxiliary bracket 127 is pivotally supported on the main bracket 120 andis provided with a front fork 128 and a tail piece 129 which supports anadjustable threaded screw 132 that is held in position against casualdisplacement by means of a lock washer 134.

The components that comprise the amplifier are mounted on a smallcomponent board or panel 140 which is secured at its four corners tofour bosses 142A, 142B, 142C and 142D formed on the inner surface of thefront wall of the housing 25, as may be seen upon reference to FIGS. 6and 7.

The component board 140 is provided with an opening or window 146 toleave an open space to accommodate the housing for the switch at therear of the microphone assembly 60. This switch 125 is held in fixedposition on the supporting bracket 120 by any suitable means indicatedas a lock washer 148, to hold the front end of the switch at itsoperating button spaced a short distance at the back of the microphoneassembly, so the lost motion movement backward of the microphoneassembly when pressed against a human body will be sufficient to operatethe switch button to close the switch 125 against the conventionalreaction spring which normally holds the switch in open position.

The backward motion of the microphone assembly 60 to operate the switch125 is accomplished by means of the Pivoted arm 128 previously referredto.

On the component board or panel is also mounted a U-shaped bracket whichis suitably secured to and mounted on the component board 140 by acouple of screws 162. The bracket 160 serves to support two controlknobs 164 and 166 for two separate variable resistors of the amplifiercircuit, which will be illustrated in FIGURE 8, to provide individualcontrol of tone or frequency range and control of gain for theamplifying system.

As shown in FIGURE 6 the main housing and control handle 25 is providedwith a rear cover 170 which nests on and fits over the rear peripheralrim edge of the front part of the housing 25 as indicated by theshoulder rim 172. That rear cover 170 is provided with two openings 174and 176 of which only one is shown in FIGURE 6, but which areappropriately disposed to permit the control knobs 164 and 166 to extendbackward through those two openings 174 and 176 to be accessible foroperation by the thumb of the operator conducting the auscultation.

The lower part of the housing and handle 25 is provided with a lowercompartment 180 to receive two dry cell batteries and 186 that are tosupply power for the stethoscope.

The lower compartment 180 is separated from the upper compartment of thehousing 25 by a wall 188. At the lower part of the compartment 180 aflexible U-shaped contact 189 is provided having two seating contacts189A and 189B against which the ends of the two respective batteries 185and 186 may be seated to establish electrical contact. The opposite endsof the two batteries 185 and 186 engage corresponding contact lements192A and 192B which are connected to fixed electrical terminals 194A and194B shown in dotted outline behind the component board 140. TheU-shaped contact 189 is shown suitably supported on two bosses 195A and195B.

As will now be understood, upon referring to FIG- URE 3, FIGURE 3A andFIGURE 6, upon pressure of the front plate 70 of the microphone assembly60 against the human body indicated at 80, the first reaction will occuras in FIGURE 3A to cause the small area of the human skin 78 to enterthe opening 76 to press the button 65 backward slightly to lower thearmature or diaphragm 44 closer to its related core 42.

Small additional pressure of the microphone assembly 60 against the bodybeing examined, will then take up some of the resiliency of the rubbersupporting cup 116 to enable the rear pressure plate 70A to pressagainst the fork 128 of the bracket 127 to the extent permitted by theadjustable back screw 134 in the tail piece of the bracket 127,whereupon the pressure against the front bracket piece 128 will operatethe switch 125 from its normal open position to closed position to closethe circuit through the switch. The circuit through the switch will thusremain closed so long as the pressure is maintained by the examiningoperator on the microphone assembly 60 by pressure on the housing 25.

The pressure required on the microphone assembly 60 to operate theswitch 125 will be very little, and particularly less than will move thefront face of the pressure plate 70 backward suificiently to permit thefront face of the flange 116D to reach and engage the surface of thhuman body being tested.

The pressure required to operate the microphone for operation of thestethoscope to close the switch 125 which then connects the amplifierinto circuit with the microphone will be sufiiciently small so that itmay be readily accomplished by the examining physician without anystress that would be distractive.

At the same time, the tone control and the gain control knobs 164 and166 may be readily operated by the thumb of the examining physician sothat he may adjust th amplifier to adjust its sensitivity in thefrequency range and in the gain in order to enable the examiningphysician to obtain optimum conditions for aural observation of thesignal representative of the sound for which he is listening.

In FIGURE 8 is shown a simple diagram of the amplifier. The powermicrophone 60 when operated by the external sound generates the signalwhich is then supplied through a coupling capacitor C1 to the input orbase circuit of a first transistor Ql. Bias voltage for the base emittercircuit is derived from a voltage divider including two resistors R land R2 energized through a load-limiting resistor R3 from the batteryB-l corresponding to the two cells 185 and 186 shown in FIG- URES 6 and7.

Transistor Q]l is also provided with collector resistor R-4 and anemitter resistor R-S provided with a by-pass capacitor C-3. A capacitorC-2 is connected between the base and the collector electrodes of Q-l. Acoupling capacitor C4 couples the Q-l collector to the base or" a secondtransistor Q2. The bias for the base emitter circuit of Q-Z is providedby a voltage divider including two resistors R-6 and R-7, with the baseof Q-2 connected to the juncture point between those two resistors. Asmall capacitor C is disposed between the base terminal and thecollector terminal of Q2, for isolation purposes. The transistor Q-2 isprovided with a collector resistor R8 and an emitter resistor R-fil,which latter is provided with a by-pass capacitor C-6.

The collector terminal of the transistor Q-Z is coupled to the input orbase terminal of a third transistor Q3 through a coupling capacitor C-7and a variable resistor or poteniometer R-ltl which is to serve as avolume control, and is controlled by the gain control knob of FIG- URES6 and 7.

A tone control circuit is provided including a capacitor C-3 and avariable resistor potentiometer R-li connected as shown to the output ofthe coupling capacitor C7. That tone control resistor R-ll is controlledby the knob 164 shown in FIGURES 6 and 7.

The output of the transistor Q3 from its collector terminal is fed intoa pair of headphone receivers corresponding to receivers 32 and 34 ofFIGURE 1. A resistor R-IZ provides bias voltage for the transistor Q-3through the headphones 32 and 34.

The switch shown connecting the battery B-l to the 8 power buss line forthe amplifier system corresponds to the switch shown in FIGURE 6.

Since transistors are utilized in the amplifier system, instantaneousoperation of the system is available upon closure of the switch 125. Inthis case, since vacuum tubes are not employed, no heating up time isrequired for the filaments, and the switch 125 may be utilized so thatthe stethoscope is in operation automatically only when the microphoneis pressed against a human body sufficiently to close the switch. Uponremoval of the microphone from one area of a body to be placed against aSubsequent area of the body the switch automatically opens anddisconnects the battery from the various resistors which would otherwisecause an unnecessary drain on those batteries. The automatic feature ofconnecting the battery to the microphone and the amplifier is one of theimportant features of this invention.

The large capacitor C-9 is provided as a by-pass to keep the alternatingcurrent signals out of the battery to further assure its long life.

The values of the resistors and of the capacitors and the identificationof the transistors that have been employed in a system, embodying theinvention, as shown, are as follows:

wwwwwwwwwwww The invention thus described provides a simple electricallyoperated stethoscope in which particularly a very small light weightmicrophone has been modified to prevent the occurrence of any resonanceconditions in the microphone within the range of frequencies to becovered in an auscultation examination of a human body.

Obviously, the microphone as modified herein to shift the natural orresonance frequency of a microphone diaphragm to a region beyond therange under examination, provides a feature that may be advantageouslyutilized in many other applications where vibration problems or frequency problems are to be studied.

The invention therefore is not limited in any way merely to theapplication illustrated nor -to the specific details of constructionthat are shown merely by way of example, since it is clear that theinvention may be varied and modified in various ways without departingfrom the spirit and scope of the invention as set forth in the appendedclaims.

What is claimed is:

1. An audio cardioscope or electronic stethoscope, comprising anelectromagnetic microphone transducer to be placed against a human bodybeing examined, said transducer including a magnetic core, a vibratablearmature, and a coil on the core to develop an output voltage inresponse to vibration of the armature; an amplifier to be energized bythe output voltage from said transducer and serving to develop anamplified output signal related to the frequency of the output voltagefrom the transducer;

a head-phone receiver to be energized by the amplified output signalfrom said amplifier;

and means supported on and associated with said vibratable armature ofsaid transducer for physically coupling the mass of the human body tosaid armature during auscultation of said human body, said meansincluding a button of sound conducting material supported co-axially onsaid vibratable armature and shaped to have a front end of relativelypoint form for engaging such human body, and further including apressure plate having a bore co-axial with the point of said button tolimit the amount of protrusion of the engaged skin axially against saidbutton, and further including means for limiting inward axial movementof said button to maintain at least a minimum air gap between saidarmature and the core.

2. An electronic stethoscope, as in claim 1, in which said couplingmeans between the transducer armature and the human body consists of amass element secured to the armature at a central area of symmetryclosely adjacent the mass center of the armature and shaped to expose aprojecting front end of minimal area for engaging a point on the humanbody to be examined by auscultation, whereby a limited amount of theskin where engaged will protrude into the opening and press the masselement gization of the amplifier, said electrical switch means beingoperable to closed position by the pressure of applying the microphoneto the surface of the body being examined, and said electrical switchbeing normally returnable to open position by release of said applyingpressure.

5. An electronic stethoscope as in claim 4, including a supporting cupof rubbery material for supporting the microphone and for providing asmall amount of lost motion for the microphone as the microphone ispressed against a human body for auscultation, said lost motion beingsulficient to operate said switch means.

6. An electronic stethoscope, as in claim 5, in which said supportingcup consists of a first cylinder anchored to a structure and a secondcylinder reentrant to said first cylinder and supporting the microphone,said double cylinder construction of rubbery material having sufiicientresiliency to proto shift the armature center towards the core to definea smaller initial air gap. 3. An electronic stethoscope, as in claim 2,including, additionally,

a stop element to limit the shifting movement of the armature towardsthe core and to hold the armature vide the necessary lost motion toelfect the switch operation.

References Cited by the Examiner UNITED STATES PATENTS center at suchfixed limit stop point whereby the 1,658,327 2/1928 Dodge 1791 humanbody serves to hold the center region of the 2,159,533 5/ 1939 Rayment18124 armature at fixed spacing of the air gap. 2,169,806 8/ 1939 Lianet a1 18124 4. An electronic stethoscope comprising 2,614,646 10/1952Eaton 18124 a microphone to be applied to the surface of a human2,755,336 7/1956 Zener 179-l body to be examined, and including meansfor gen- 2,820,107 1/1958 Knauert 179-115 crating a signal according toa sound affecting the 2,343,560 8/1958 Wiegand t 1 179 115 microphone;3,087,016 4/1963 Dahl 179-1 a signal amplifier to amplify the signalfrom the microphone; ROBERT H. ROSE, Primary Examiner.

sound reproducing means to be energized by the signal from theamplifier; and electrical switch means for controlling the ener- WILLIAMC. COOPER, Examiner.

A. J. SANTORELLI, R. MURRAY, Assistant Examin rs.

1. AN AUDIO CARDIOSCOPE OR ELECTRIC STETHOSCOPE, COMPRISING ANELECTROMAGNETIC MICROPHONE TRANSDUCER TO BE PLACED AGAINST A HUMAN BODYBEING EXAMINED, SAID TRANSDUCER INCLUDING A MAGNETIC CORE, A VIBRATABLEARMATURE, AND A COIL ON THE CORE TO DEVELOP AN OUTPUT VOLTAGE INRESPONSE TO VIBRATION OF THE ARMATURE; AN AMPLIFIER TO BE ENERGIZED BYTHE OUTPUT VOLTAGE FROM SAID TRANSDUCER AND SERVING TO DEVELOP ANAMPLIFIED OUTPUT SIGNAL RELATED TO THE FREQUENCY OF THE OUTPUT VOLTAGEFROM THE TRANSDUCER; A HEAD-PHONE RECEIVER TO BE ENERGIZED BY THEAMPLIFIED OUTPUT SIGNAL FROM SAID AMPLIFIER; AND MEANS SUPPORTED ON ANDASSOCIATED WITH SAID VIBRATABLE ARMATURE OF SAID TRANSDUCER FORPHYDICALLY COUPLING THE MASS OF THE HUMAN BODY TO SAID ARMATURE DURINGAUSCULTATION OF SAID HUMAN BODY, SAID MEANS INCLUDING A BUTTON OF SOUNDCONDUCTING MATERIAL SUPPORTED CO-AXIALLY ON SAID VIBRATABLE ARMATURE ANDSHAPED TO HAVE A FRONT END OF RELATIVELY POINT FORM FOR ENGAGING SUCHHUMAN BODY, AND FURTHER INCLUDING A PRESSURE PLATE HAVING A BORECO-AXIAL WITH THE POINT OF SAID BUTTON TO LIMIT THE AMOUNT OF PROTRUSIONOF THE ENGAGED SKIN AXIALLY AGAINST SAID BUTTON, AND FURTHER INCLUDINGMEANS FOR LIMTING INWARD AXIAL MOVEMENT OF SAID BUTTON TO MAINTAIN ATLEAST A MINIMUM AIR GAP BETWEEN SAID ARMATURE AND THE CORE.